1. Field of the Invention
The present invention relates to pressure measurement devices. More specifically, the present invention relates to pressure transducers based on solid-state strain gauge devices.
2. Description of the Related Art
Pressure transducers are devices that convert pressure to an electrical signal, and are commonly used to measure fluid and gas pressures. For example, pressure transducers might be used to monitor ink levels in an inkjet printer or to measure the air pressure in a tire.
A conventional strain gauge based pressure transducer typically includes a cylindrical housing that is separated into two chambers by a thin, flexible diaphragm. The first chamber is coupled to the medium being measured, and the second chamber is set to a known reference pressure, such as atmospheric pressure. The diaphragm flexes slightly into one chamber or the other depending on the difference in pressure between the chambers. A strain gauge (a device whose resistance changes depending on the amount of strain placed on it) is attached to the diaphragm such that the flexure of the diaphragm introduces a strain on the gauge. The strain gauge then generates an electrical output signal that has a well-defined relationship to the pressure in the medium.
In certain applications, the pressure transducer may be left under load for a long time period before a measurement is needed. For example, a missile typically includes vessels charged with gas. After assembly, the missile may be held in storage for a long period of time (up to ten years) before being placed in operation. During this period, the gas may leak. If the required amount of gas is not present, the missile will fail to operate properly. It is therefore critical to accurately determine the amount of gas remaining in the missile just prior to operation, after a potentially long storage period (without disassembling the missile).
Conventional pressure transducers are not suitable for applications such as the one described above because solid-state strain gauge devices—such as a semiconductor Wheatstone bridge or piezoelectric wafer—are known to be susceptible to signal errors such as drift and hysterisis when left under load for extended periods of time. This drift is due to creep of the transducer substrate and transducer element materials. These transducers are also susceptible to damage from pressure shocks or “spikes” which can permanently deform or even rupture the electronic transducer element.
Hence, a need exists in the art for an improved system or method for measuring pressure that retains accuracy when subject to long term loads or pressure shocks.